Over recent years, various types of projectors employing laser light sources have been proposed and gathered much attention as next-generation high quality visual display devices from the viewpoint of ensuring a color reproduction range wider than that of conventional projectors employing discharge lamps as light sources.
When laser light is projected on a transmission-type screen or a reflection-type screen, due to interference of the laser light, a projected image looks floating above the screen or speckles appear on the screen as mottle noises. These speckles are desirably as small as possible since the observer's eyes are dazzled thereby, resulting in a problem in visual confirmation of the projected image and in a decrease in visual quality.
In Patent Document 1 listed below, in a scanning-type laser projector, a birefringence plate is arranged between a scanning member and a screen and the optical axis of the birefringence plate is positioned to be declined with respect to the polarization direction of laser light. Speckle patterns produced by two polarization-separated laser lights are superimposed to reduce speckle contrast.
In Patent Document 2 listed below, in a rear projection-type display employing a laser light source, a screen is rotated parallel to the image plane to reduce speckles or scintillation.
In Patent Document 3 listed below, in a rear projection-type display, a projection lens is minutely vibrated in the direction perpendicular to the optical axis to reduce speckles or scintillation.    Patent Document 1: Unexamined Japanese Patent Application Publication No. 2006-284749    Patent Document 2: Unexamined Japanese Patent Application Publication No. 2006-343663    Patent Document 3: Unexamined Japanese Patent Application Publication No. 2003-21806